Acute lymphocytic leukemia (ALL) is the most common malignancy of childhood. Currently about 50% of children diagnosed as having ALL will survive for 5 or more years. With improved survival times, many serious adverse effects of cancer therapy are being manifested: some of these are leucoencephalopathy, disrupted growth and development and neuroendocrine dysfunction. At present it is uncertain whether one can predict which children will experience these particular adverse effects and what if anything can be done to prevent expression of hormone dysfunction. The specific objectives are: 1. To establish if at any stage of therapy for ALL, there is an impairment of the neuroendocrine-endocrine end-organ axis, and to what extent such impairment is exposed clinically by disturbed growth and development. 2. To establish the relative "necessity" and "potential benefit" of appropriately timed trials of exogenous hormone therapy based on the temporal characteristics of these endocrine disruptions. Methods will involve a four-year prospective evaluation of newly diagnosed children with ALL. The new patients will be enrolled during the first 2 years of the study, allowing 2-3 year follow-up for the survivors. Each patient will be evaluated by extensive, sequential anthropometric parameters, bone age analyses, and basal and "stress"-released hormone levels, measured at each phase of cancer therapy.